C3 and C4 Plants

C3 and C4 plants

C3 and C4 plants are two distinct groups classified based on their primary pathways of carbon fixation during photosynthesis. 

  • C3 Plants:

- Carbon Fixation:

C3 plants utilize the Calvin cycle as their primary pathway for carbon fixation.

The first stable product of CO2 fixation is a 3-carbon compound, 3-phosphoglyceric acid (3-PGA). 

- Leaf Anatomy:

Mesophyll cells in C3 plants conduct both the Calvin cycle and initial CO2 fixation.

They lack specialized leaf anatomy like Kranz anatomy found in C4 plants. 

- Examples:

Common examples of C3 plants include rice, wheat, oats, and soybeans. 

  • C4 Plants:

- Carbon Fixation:

C4 plants initially fix CO2 into a 4-carbon compound, oxaloacetic acid (OAA), via the Hatch and Slack pathway.

The Calvin cycle, occurring primarily in bundle sheath cells, synthesizes sugars from CO2 released by the breakdown of OAA. 

- Leaf Anatomy:

C4 plants exhibit Kranz anatomy, characterized by bundle sheath cells surrounding vascular bundles.

Mesophyll cells primarily facilitate the C4 pathway for initial CO2 fixation. 

- Physiological Traits:

Adapted to hot and dry environments, C4 plants demonstrate higher photosynthetic efficiency, resilience to high temperatures, and reduced photorespiration compared to C3 plants. 

- Examples:

Notable examples of C4 plants include maize, sugarcane, sorghum, and certain grass species. 

  • Comparison:

- Carbon Fixation Efficiency:

C4 plants exhibit higher carbon fixation efficiency due to the concentration of CO2 around Rubisco enzyme in bundle sheath cells.

C3 plants are less efficient in carbon fixation, especially under hot and dry conditions. 

- Water Use Efficiency:

C4 plants typically have higher water use efficiency due to reduced photorespiration, making them well-suited for arid environments.

C3 plants may experience water loss through increased stomatal opening for CO2 uptake during photorespiration. 

Environmental Adaptations:

C4 plants thrive in warm, dry climates with intense sunlight, while C3 plants are more common in cooler, moist environments.